1. Field of the Invention
This invention relates to material appropriate for protective films and to a magnetic head comprising a protective film made of the material.
2. Description of the Related Art
Hitherto, protective films of magnetic heads, thin film elements, etc., have been formed on the elements to be protected by using thin film formation technology.
For example, with conventional inductive magnetic heads, a protective film is placed on a slide face with a magnetic recording medium, in order to prevent abrasion of a detection section formed by a core and gap. Specifically, a protective film is formed by thin film formation technology such as sputtering on a substrate, such as a ceramic, on which a magnetic film forming a core and a nonmagnetic film forming a gap are laminated.
The requirements for the protective films to exhibit sufficient protection performance often include a small thermal expansion coefficient difference, a small hardness difference, etc., between the protective film and the object to be protected, in addition to excellent hardness and high stability in water of the protective films.
For example, it is desired that a protective film placed on the slide face of a magnetic head provides a small thermal expansion coefficient difference between a substrate and the protective film, the same degree of hardness as the substrate, fast film formation speed, excellent stability in water, etc.
Hitherto, materials such as SiO.sub.2 glass, glass phosphate, alumina, tantalum oxide, silicon carbide, and forsterite have been used for such magnetic head protective films. The materials are reported in Japanese Patent Laid-Open Nos. Sho 58-26308, 61-24007, and 63-241711 and Hei 4-344307.
However, if conventional SiO.sub.2 glass, glass phosphate, alumina, tantalum oxide, or silicon carbide is used as a magnetic head protective film, any of the following problems may arise:
First problem: Since the thermal expansion coefficient difference between a substrate and protective film is large, a large stress is caused by a thermal history. Thus, a crack occurs not only on the protective film but also on the substrate on the core. PA1 Second problem: Since the hardness difference between a substrate and core and a protective film is large, partial abrasion occurs between the substrate and core and protective film when the slide face of a magnetic head is ground or when the magnetic head and magnetic recording medium slide with each other. PA1 Third problem: When protective films are made of the above mentioned materials, it takes a long time to form the film and time; the materials are not conducive to mass production at low cost. PA1 If forsterite is used as a magnetic head protective film, it provides more advantageous characteristics than the above-mentioned materials with respect to the thermal expansion coefficient, hardness, and film formation speed, but it is unstable in water and is altered in quality due to grinding fluid applied during a grinding process so that the advantageous features degrade.